The present invention relates to angular position sensors.
Power assisted steering is a standard motor vehicle equipment feature. It happens that in order for a typical power steering control system to properly operate, a steering column torque sensor must be included in the system to close the control loop. Torque sensors, such as resistance strip/strain gauge sensors, capacitance sensors, eddy-current sensors, magneto-elastic sensors, and transformer/strain gauge sensors, have been provided to determine the torque on the steering column. However, these sensors lack the sensitivity required for many of the present power steering control systems. Moreover, these sensors are extremely sensitive to changes in temperature and have limited durability.
Because of the high durability requirement, non-contact sensing technology is utilized. A typical non-contact sensor includes one or more magnetic field sensors, e.g., magnetoresistive sensors or Hall effect sensors, placed in proximity to a magnet, e.g., permanent or electrical. An electrical magnet provides constant magnetic field strength, but requires additional electronics that increase costs and the likelihood of sensor failure. On the other hand, a permanent magnet is simpler and more cost effective, but the field strength is very temperature dependent and can degrade over time.
The present invention understands that in order to compensate for temperature effects and degradation effects, linear Hall sensors can be used. Moreover, the present invention understands that a linear Hall sensor can be programmed with a temperature coefficient to match the temperature coefficient of a corresponding permanent magnet in order to compensate the sensor output for any effects caused by changes in temperature. Unfortunately, due to material variations in permanent magnets, programming a Hall sensor with a static temperature coefficient can result in the limited accuracy of the, e.g., angular position sensor in which the Hall sensor/permanent magnet configuration is used.
The present invention has recognized the above-mentioned prior art drawbacks, and has provided the below-disclosed solutions to one or more of the prior art deficiencies.
A method for temperature compensating the output of an angular position sensor includes providing at least two magnetic field sensors. A magnet is placed so that it is equidistant from the sensors. Thereafter, the magnet is rotated and outputs from the sensors are received. Based on the output from the sensors, a compensation signal is generated.
In a preferred embodiment, the compensation signal is sent to a control system. Preferably, the outputs of the sensors are ninety degrees out of phase with each other. In a preferred embodiment of the present invention, the compensation signal is generated by determining the square root of the sum of the squares of the outputs.
In another aspect of the present invention, an angular position sensor assembly includes a magnet. A first sensor and a second sensor are placed in proximity to the magnet. The first sensor provides a first output signal and the second sensor provides a second output signal that is ninety degrees out of phase with the first output signal. In this aspect of the present invention, a processor receives the output signals and generates a temperature compensation signal in response thereto.
The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: